1. Field of the Invention
This invention relates to a display apparatus for a vehicle, and more particularly to a display apparatus for a vehicle for passing light from a light emitting source through a front glass provided at an opening of a dash board incorporating the light emitting source and a semi-permeable combiner having a polarizing plate in this order, thereby guiding the light to a view point of a driver (driver's view point).
2. Description of the Related Art
There is a previously known display apparatus for a vehicle, in which, in order to display a displaying image as a virtual image at a long distance in front of a vehicle, as seen from FIG. 1, a display device 11 for information display with the display surface oriented above is arranged in e.g. a dash board, and the light emitted from the display device 11 is reflected from the semi-permeable combiner 12 so that it is guided to the driver's view point, thereby visually recognizing the virtual image of the display device 11 behind the semi-permeable combiner 12, i.e. in front of the vehicle.
In the display apparatus for a vehicle described above, however, the semi-permeable combiner 12 includes a semi-permeable resin 12a and a polarizing plate 12b. Between the semi-permeable combiner 12 and the display device 11, another polarizing plate 14 is arranged which has a polarizing direction perpendicular to that of the polarizing plate 12b. 
By arranging the polarizing plates 12b and 14 in this manner, external light such as sunlight does not reach the display device 11, thereby preventing the display device 11 from “washing out” owing to the external light. In addition, the light emitted from the display device 11 does not reach a windshield 15, thereby preventing the display device from being reflected oh the window shield 15.
In the display apparatus for a vehicle described above, a previously known typical warning display unit 16 is further arranged behind the semi-permeable combiner 12. This warning display unit 16 serves to light a symbol mark with no design. The light emitted by the warning display unit 16 is guided to the view point of the driver (driver's view point) through the semi-permeable combiner 12.
A front glass 18 is arranged at an opening of the dash board 17 which incorporates the warning display unit 16. The front glass 18 is subjected to semi-permeable processing by e.g. smoking (coating of a smoke film) in order to prevent the external light from reaching the display device 11 so that the display device 11 is washed out.
As described above, the front glass 18 is subjected to the permeable processing to prevent the wash-out of the warning display unit 16. However, the light emitted from the warning display unit 16 must permeate two semi-permeable members of the front glass 18 and combiner 12 to reach the driver's view point. This makes it difficult to assure the luminance.
In order that the light emitted from the warning display unit 16 can be surely recognized, the luminance of the warning display unit 16 can be set at a high value. This is however problematic in cost.